EP0366796A1

EP0366796A1 - Activated carbon and process for its production

Info

Publication number: EP0366796A1
Application number: EP88910105A
Authority: EP
Inventors: Takahiro Kasuh; Gunji Morino
Original assignee: Osaka Gas Co Ltd
Current assignee: Osaka Gas Co Ltd
Priority date: 1987-11-20
Filing date: 1988-11-21
Publication date: 1990-05-09
Anticipated expiration: 2008-11-21
Also published as: EP0366796A4; US5143889A; DE3853824D1; DE3853824T2; JPH01230414A; WO1989004810A1; EP0366796B1

Abstract

A process for producing activated carbon by activating mesocarbon microbeads, activated carbon obtained by the process, a process for producing a carbonaceous material having a molecular sieve function, and the carbonaceous material produced by the process are disclosed. The carbonaceous material is produced by adsorbing vapor of a polymerizable organic substance on the surface of the activated mesocarbon microbeads and polymerizing the organic substance on said surface.

Description

The present invention relates to processes for preparing active carbon from meso-carbon microbeads, processes for preparing carbon materials able to achieve molecular sieve effect from the microbeads, and the obtained active carbon and carbon materials able to achieve molecular sieve effect.
The term "activated meso-carbon microbeads" used in this specification is intended to include activated meso-carbon microbeads granulated with a suitable binder as well as the activated meso-carbon microbeads per se.
Active carbon has been used long for removal of impurities and recovery of useful substances from liquids and gases because of its high adsorptivity. Stated more specifically, active carbon is used for treatment of tap water (deodorization and decoloration), decoloration of foods, removal or recovery of organic solvents or recovery of precious metals from solutions of precious metal salts, or as carriers for catalysts, antidotes, molecular sieves for separation of air, materials for batteries or the like.
Conventionally active carbon has been prepared from organic wastes such as resin wastes, residues from pulp production, coal, coal coke, wood, coconut shells or the like. For activation, selective oxidation has been performed in the presence of water vapor, air, oxygen or like oxidizer to form pores. Alternatively activation is effected by combining the hydrogen and oxygen contained in a cellulosic substance in the presence of zinc chloride to form water such that the carbon skeleton is retained. The active carbon prepared in this way maintains the original structure of starting material, and therefore includes the mesopores of 20 to 200 A in pore diameter and macropores of 200 A or more in pore diameter as well as the micropores of 20 A or less in pore diameter which participate directly in the adsorption. Such active carbon requires much time in adsorption because due to the presence of micropores in mesopores or macropores, a substance to be adsorbed is required to pass the mesopores or macropores from outside the active carbon to diffuse over the micropores. These methods result in preparation with a low activation efficiency. Even in case of a yield of about 20 to about 30% based on the starting material, the carbon is activated only to a maximum specific surface area of about 1500 m²/g.
When filled in"an adsorbing device, the active carbon derived from crushed coal or coke serving as the starting material is packed too closely because of its crush-type shape, disadvantageously involving a great pressure loss in the device.
Recently fibrous active carbon was developed and found extended applications owing to its peculiar properties and shape. However, fibrous active carbon which is prepared from cellulose, polyacrylonitrile, phenolic resin, pitch or like materials is obtained in a pronouncedly low yield by the activation process, therefore at high costs with limited applications.
A variety of zeolite are used as an adsorbent capable of selectively adsorbing only the molecules of particular size, namely as a material having an ability to achieve molecular sieve effect. Yet zeolite has the drawback of adsorbing water vapor in preference due to its high affinity for water, markedly lowering within a short time the ability to adsorb the desired substance.
During Showa 40's (1965-1974), the development of carbon-type molecular sieves was initiated. Since the period, numerous methods for preparing molecular sieves have been proposed. Various materials have been proposed for use as carbonaceous base materials among which coconut shells or like active carbon is now chiefly used (e.g. Japanese Examined Patent,-Publication No.37036/1974). Depending on the combination of materials to be separated by molecular sieves such as N2/02, C0_2/butane, n-butane/isobutane, etc., it is necessary to reduce the inherent pore size of carbonaceous base material. For this purpose, various methods have been proposed which include as a CVD method in which hydrocarbon is thermally decomposed and deposited on the surface of particulate carbonaceous base material (Japanese Unexamined Patent Publication No.130226/1981, etc.), a method in which the carbonaceous base material is impregnated with an organic substance and carbonized (Japanese Unexamined Patent Publication No.106982/1974, etc.),,a method in which a phenolic resin is adsorbed on a carbonaceous base material and is polymerized and carbonized thereon (Japanese Examined Patent Publication No.37036/1974), and a method in which a carbonaceous base material is directly activated (Japanese Unexamined Patent Publication No.182215/1981).
The carbonaceous molecular sieves prepared by these methods have pores having a size distribution in the vicinity of 4 Å. Consequently when such carbonaceous molecular sieves are used for separation of, e.g. N₂ (moleular size 3.0 A) and 0₂ (molecular size 2.8 A), the separation is performed utilizing the difference therebetween in the rate of diffusion into pores which difference occurs due to the minute difference therebetween in the molecular size. These conventional carbonaceous molecular sieves bring about a great difference within a short time after outset of adsorption in the adsorption amount between substances to be adsorbed, but each adsorption amount approaches an equilibrium one with a lapse of time. Since there is no marked difference in the equilibrium adsorption amount between N₂ and 0₂ ("Compilation of Pressure-swing Adsorption Techniques", edited by Toshinaga KAWAI and published by Industrial Technology Association), a pressure swing must be conducted at a short interval of about 1 minute when such carbonaceous molecular sieve is used in a pressure-swing adsorption (PSA) process (e.g. Japanese Examined Patent Publication No.25969/1963). This requires the operation of a pump at an increased frequency for adsorption and removal and employs a larger amount of N₂ gas for purging, incurring higher operational costs.
Conventional carbon materials used as molecular sieves for adsorption of 0₂ exhibit an adsorption volume of about 5.0 to about 7.5 ml/g and is so limited due to the pore volume of base material itself. Depending on this value, the dimensions of adsorption column in a PSA device are determined.

Means for Solving the Problems

In view of the aforesaid state of the art, we conducted extensive research on the preparation of carbon materials and molecular sieves for adsorption from new materials, and found that when meso-carbon microbeads are used as the starting material, the problems of conventional techniques can be substantially overcome or markedly alleviated.
According to the present invention, there are provided active carbon and carbon materials having an ability to achieve molecular sieve effect, and processes for preparing them, as listed below:

(1) a process for preparing active carbon, characterized by activating meso-carbon microbeads;
(2) a process for preparing active carbon as described in item (1) in which an activating auxiliary is deposited on the surface of meso-carbon microbeads before activation;
(3) a process for preparing active carbon as described in item (2) in which the activating auxiliary is at least one member selected from the group consisting of KOH, NaOH, CsOH, ZnCl₂, H₃P0₄, K₂SO₄ and K₂S;
(4) a process for preparing active carbon as described in item (2) in which a surfactant is used in depositing the activating auxiliary;
(5) a process for preparing active carbon as described in item (1) in which the act-ivation is performed in an oxidizing atmosphere without use of activating auxiliary;
(6) active carbon prepared from activated meso-carbon microbeads and having pores, the active carbon being characterized in that
- (i) the carbon is optically anisotropic,
- (ii) 90% or more of the whole of carbon consists of particles 80 pm or less in particle size, and
- (iii) the micropores of 20 A or less in pore diameter constitute 85% or more of the entire pore volume;
(7) a process for preparing a carbon material having an ability to produce molecular sieve effect, characterized in that a vapor of polymerizable organic substance is adsorbed on the surface of activated meso-carbon microbeads and is polymerized on the surface thereof;
(8) a process for preparing a carbon material as described in item (7) in which the polymer being formed during polymerization or the polymer formed thereby is carbonized; and
(9) a process for preparing the active carbon having the ability to achieve molecular sieve effect as described in item (7) in which the polymerizable organic substance is a vinyl group-containing compound.
(10) a carbon material prepared from activated meso-carbon microbeads as the base material, having pores and capable of exhibiting molecular sieve effect, characterized in that
- (i) the carbon is optically anisotropic,
- (ii) 90% or more of the whole of carbon consists of particles 80 pm or less in particle size,
- (iii) the micropores of 20 A or less in pore diameter constitute 85% or more of the entire pore volume; and
- (iv) the size of pore inlet is reduced by the polymer of polymerizable organic substance adsorbed on the surface thereof.

Recently it has been found that spherulites having reticular layers of 6-membered carbon ring superposed in parallel over each other are formed in the pitch during heating of petroleum-type or coal-type pitch in preparation of needle coke or carbon fibers from the pitch. The spherulites form a phase different from the phase of matrix pitch and can be isolated by anti-solvent method, centrifugal separation method or the like. The separated spherulites, generally termed meso-carbon microbeads, are spherical bodies about 3 to about 60 um in diameter and about 400 to about 4,500 m²/g in specific surface area and have optically anisotropic structure. With such peculiar shape and properties, the meso-carbon microbeads are expected to find use as new materials for production of high-performance materials. Nevertheless the mesocarbon microbeads have been so far used merely as starting materials for manufacture of high-density carbon materials.
Our research revealed that if the meso-carbon microbeads are activated, carbon materials such as active carbon having an utterly new shape and properties can be produced from the activated meso-carbon microbeads.
Described below in detail are an invention on a process for activating meso-carbon microbeads and on active carbon prepared from said meso-carbon microbeads (hereinafter referred to as "first invention") and an invention on a carbon material capable of producing molecular sieve effect and prepared by treating the activated meso-carbon microbeads with a vapor of polymerizable organic substance (hereinafter referred to as "second invention").

I. First Invention

In the first invention, meso-carbon microbeads are activated as they are or as provided on the surface thereof with an activating auxiliary. Examples of the activating auxiliary are KOH, NaOH, CsOH, ZnCZ2, H₃P0₄, K₂SO₄, K₂S, etc. At least one of them is used. A preferred amount of the activating auxilliary used is about 1 to about 10 times the weight of meso-carbon microbeads. Since the degree of activation is substantially in proportion to the amount of activating auxiliary used, the specific surface area of the active carbon can be varied by varying the amount thereof. An activating auxiliary such as KOH which is solid at room temperature is used preferably in the form of an aqueous solution. On the other hand, there is no special need for providing as an aqueous solution an activating auxiliary such as H₃P0₄ which is liquid at room temperature.
To improve the "wettability" of activating auxiliary on the surface of meso-carbon microbeads, acetone, methyl alcohol, ethyl alcohol or the like may be conjointly used as a surfactant. A preferred amount of the surfactant used is about 5 to about 10% based on the total amount of meso-carbon microbeads and an activating auxiliary or a solution containing an activating auxiliary.
Activation is done by heating meso-carbon microbeads with or without an activating auxiliary deposited thereon to a temperature of about 400 to about 1200°C. The rate of elevating the temperature and the heat-retaining time are not specifically limited. Usually on heating to said temperature, the microbeads are immediately cooled or held at the same temperature for about 3 hours or less. The activation is effected in any of inert atmospheres such as nitrogen or argon atmosphere, and oxidizing atmospheres containing water vapor, carbon monoxide, oxygen or the like. In case of inert atmosphere, a higher yield is achieved.
In activation in an inert atmosphere, it is more preferred to heat the meso-carbon microbeads with an activating auxiliary deposited thereon to about 400 to about 1200°C while elevating the temperature at a rate of about 300 to about 600°C/hr and to maintain the same temperature for 30 minutes to about 1 hour.
In activation in an oxidizing atmosphere, an activating auxiliary can be used but usually need not be used. This activation is done more preferably by heating . the microbeads to a temperature of about 600 to about 900°C in the absence of activating auxiliary or to a temperature of about 400 to about 900°C in the presence of activating auxiliary, at a temperature-elevating rate of about 300 to about 600°C/h, followed by maintaining the same temperature for about 2 to about 3 hours. Care should be taken to avoid bumping which may occur in use of activating auxiliary.
Our research shows that an optimum activating temperature exists for every activating auxiliary. For example, optimal activating temperatures are about 800 to about 1000°C for KOH, K₂S0₄ and K₂S, about 600°C for NaOH and CsOH, and about 450°C for ZnCl₂. After activation, the meso-carbon microbeads are cooled to room temperature, washed with water to remove the unreacted activating auxiliary and the reaction product of activating auxiliary and dried to provide a carbon material according to the first invention.
In the first invention, the activating auxiliary is presumed to promote the oxidative gasification of the carbon in the meso-carbon microbeads. Stated more specifically, the activating auxiliary is reacted with the carbon atoms of reticular layers of 6-membered carbon ring constituting the meso-carbon microbeads to convert the carbon into carbon monoxide or carbon dioxide, and is discharged out of the system.
In activation in an inert atmosphere, the portion having not participated in the reaction becomes carbonized, developing a difference in the structure between the reacted and unreacted portions, thereby forming pores. In this way the meso-carbon microbeads are formed with the micropores substantially 20 A in pore diameter as a whole and having a pore diameter distribution with a sharp peak in the vicinity of 13 to 14 A. In an inert atmosphere, the gas reaction at the surface of microbeads occurs with an increased selectivity, resulting in a prominent increase of yield.
The reaction of carbon and activating auxiliary in the first invention proceeds at a high intensity. In consequence, if carbon fibers are activated in place of meso-carbon microbeads according to the invention, the activated carbon fibers are deformed to a shape entirely different from the original one and imparted a significantly reduced strength. On the other hand, the activated meso-carbon microbeads retain the original spherical shape and exhibit no marked reduction of strength.
The active carbon prepared according to the first invention is optically anisotropic and include micropores 20 A or less in diameter which constitute 85% . or more of pore volume. The micropores of the active carbon is about 500 to about 4600 m²/g in the specific surface area and about 0.5 to about 3.0 ml/g in the entire pore volume. The active carbon adsorbs benzene at an adsorptivity of about 0.2 to about 1.0 g/g according to JIS K 1474 and methylene blue at an adsorptivity of about 100 to about 650 ml/g according to JIS K 1470.

II. Second Invention

In the second invention, the meso-carbon microbeads are activated in the same manner as in the first invention, and the activated ones as they are or as pelletized with a binder are treated with a vapor of polymerizable organic substance.
In case of pelletization, the meso-carbon microbeads are mixed with a binder and the mixture is shaped and dried by the conventional granulation method. Examples of useful binders are coal tar pitch, phenolic resin, methyl cellulose, bentonite, polyamide, polyimide, styrene resin, cellulose resin, acrylic resin, epoxy resin, furan resin, urea resin, melamine resin, silicone resin, starch, glue, gelatin, deacetylated chitin, etc. Among them, those commonly used for granulation can be used without specific limitation. There is no specific restriction as to the shape and size of pellets.
The polymerizable organic substances useful in the second invention are the compounds having the properties of showing a satisfactory vapor pressure in a specific temperature range, being free of thermal decomposition in a gas phase, undergoing thermal polymerization after adsorption by the activated meso- carbon microbeads in sufficient amount and becoming carbonized in a low retention temperature range lower than the thermal decomposition temperature to be described later. Examples of such compounds high in polymerizability and reactivity include vinyl group-containing compounds. Specific examples of such compounds are 5-vinyl-2-norbornane, 2-vinylnaphthalene, 4- vinylcyclohexene, 9-vinylanthracene, 4-vinylanisole, 4- vinylbiphenyl, 2-vinylfuran, 9-vinylcarbazole and like styrene derivatives. When a low-molecular weight compound such as ethylene, methane, ethane or the like is used in place of the vinyl group-containing compound, the desired effect can not be achieved because the adsorbed compound is easily removed.
The activated meso-carbon microbeads are treated with the polymerizable organic substance by the following method. The activated meso-carbon microbeads are placed in an atmosphere adjusted so that the vapor of organic substance has a concentration of about 5 to about 70% (the maximum value being substantially equal to the saturated vapor pressure), preferably about 10 to about 50%, in an inert gas such as nitrogen gas, helium gas, argon gas or the like. Then the microbeads are maintained at a temperature of about 400°C or higher and a temperature lower than the temperature for the thermal decomposition of the organic substance. When the vapor of organic substance has a concentration of less than 5% in the atmosphere, irregular adsorption of organic substance results, causing likelihood to give an uneven quality to the final product. If the maintained temperature is lower than 400°C, there occurs unsatisfactory degree of polyerization or carbonization of organic substance adsorbed on the activated meso-carbon microbeads, making it difficult to control the pore size. Reversely if the maintained temperature is higher than the temperature for the thermal polymerization of organic substance, the organic substance to be adsorbed undergoes thermal polymerization or thermal decomposition in the gas phase, and is consequently deposited as a carbon product of thermal polymerization or decomposition on the interior of pores of meso-carbon microbeads as well as on the inlet thereof, resulting in decrease of adsorption volume. In the invention, the organic substance adsorbed on the surface of meso-carbon microbeads is activated by contact with the microbeads, so that it is polymerized or carbonized at a temperature lower than the usual thermal polymerization temperature, enabling the control of pore size of meso-carbon microbeads.
The reaction is maintained under the foregoing conditions until the meso-carbon microbeads are polymerized with the organic substance, or at least part of organic substance is carbonized on adsorption of 5 to 95% by weight of organic substance based on the weight of meso-carbon microbeads. The degree of polymerization or carbonization on adsorption varies depending on the specific surface area of activated meso-carbon microbeads. For example, in case of use as molecular sieve for separation of M-_2/0₂, the polymerization or carbonization is preferably continued until the activated meso-carbon microbeads with a pore size of about 13 to about 14 A show a diminish of the BET specific surface area as determined by adsorption of N₂ from the range of about 500 to about 2000 m²/g to the range of about 2 to about 100 m²/g. If the BET specific surface area of carbon material as determined by adsorption of N₂ exceeds 100 m²/g, the meso-carbon microbeads exhibit insufficient reduction in size of pore inlet, resulting in a small difference in the amounts of N₂ and 0₂ adsorbed in pores and thus in lower degree of separation. On the other hand, below 2 m²/g, the activated meso-carbon microbeads are given pores having too small size inlets, leading to marked decrease in an absolute gas adsorption amount.
The carbon material of the second.invention is substantially equal in dimensions and shape to the carbon material of the first invention, and is optically anisotropic.
According to the process of the invention, the activating auxiliary to be used is inexpensive and the carbon materials are produced in a high yield, therefore at exceedingly reduced costs. Further, the specific surface area can be varied in a wide range of 500 to 4,600 m²/g by varying the amount of activating auxiliary used. Moreover, the carbon materials of the first invention display an adsorptivity equal to or higher than that of conventional granular active carbon under elevated pressure as well as normal pressure. The carbon materials of the first invention are useful in extremely wide areas because of their shape and properties of achieving rapid adsorption with high adsorptivity.
The pores of carbon materials according to the second invention have inlets with a size reduced to a significantly regular size despite their pore volume (adsorption volume) as large as that of the carbon materials of the first invention. Consequently the carbon materials of the second invention are very useful for selective separation of a substance having a particular molecular size from the other substance in a mixture. For example, when the carbon material of the second invention with a specific surface area of nearly zero as determined by the method for determining the BET specific surface by adsorption of N₂ is used as a molecular sieve for separation of N₂ (or 0₂ adsorbent) in N _2/0₂ gas mixture with use of a PSA device, the b₂ gas is selectively adsorbed, and the N₂ gas is adsorbed in a significantly small amount. Therefore the time interval of pressure swing can be extended to about 5 times, and it becomes possible to miniaturize to a pronounced extent the adsorption column which occupies the largest space in a PSA device. Accordingly a great economic advantage is provided.
As stated above, the carbon material of the second invention having pores with a suitably controlled inlet size adsorbs substantially only 0₂ so that the gas mixture removed from the PSA device contains O₂ in a high concentration. Accordingly the PSA device can serve also as an apparatus for enriching oxygen.
The carbon materials of the second invention can be used as molecular sieves for separation of other gas mixtures than N _Z/0₂ mixture. For every molecule, a "critical pore size" exists at which or below which the particular molecule can not be adsorbed. The critical pore size, however, can not be determined directly by the currently available measuring techniques. According to the present invention, a carbon material having an ability to produce the desired molecular sieve effect can be easily prepared in a manner set out below. In preparing the carbon material of the second invention, the producing conditions are varied and the resulting carbon materials are checked for an ability to achieve molecular sieve effect for a particular molecule. In this way, a relationship can be established between the producing conditions and the molecular sieve effect of the obtained carbon material for each"molecule.
Given below are Examples to clarify the invention in greater detail with reference to the accompanying drawings of which:

Fig. 1 and Fig. 2 are graphs each showing the particle size distribution of the mesocarbon microbeads used as a starting material in the Examples of the invention;
Fig. 3 is a graph showing an adsorption isotherm obtained by subjecting the activated carbons produced in the Examples to N₂ gas adsorption method;
Fig. 4 is a graph indicating the relationship between the amount of the KOH used and the BET specific surface area in the Examples;
Fig. 5 is a graph showing the adsorptivity of the activated carbons obtained in the Examples in respect of various compounds;
Fig. 6 is a graph showing the distribution of the pores of the mesocarbon microbeads as used in Examples;
Fig. 7 is a graph showing the ability of the carbon material to adsorb 0₂ and N₂ in the Example using styrene as an organic substance;
Fig. 8 is a flow diagram schematically showing an apparatus for determining the gas-adsorbing property;
Fig. 9 is a graph illustrating the ability of a commercially available carbon material to adsorb 0₂ and N₂;
Figs. 10 to Fig. 13 are graphs each showing the relationship between the amount of polymerized and carbonized styrene as adsorbed on activated mesocarbon microbeads and the ability of the microbeads to adsorb 0₂ and ^N ₂ ^;
Fig. 14 is a graph showing the ability of a carbon material to adsorb 0₂ and N₂ in an Example using 5-vinyl-2-norbornene as an organic substance; and
Fig. 15 is a graph showing the ability of carbon materials to adsorb Ar and 0₂ in an Example using 5-vinyl-2-norbornene as an organic substance.

Example 1

Water and acetone were added in specific amounts to a mixture of 10 g of mesocarbon microbeads having a particle size distribution as shown in Fig. 1 (weight distribution) and Fig. 2 (distribution of the number of the microbeads) and a specific amount of potassium hydroxide (activating auxiliary). The mixture was stirred homogeneously, giving a slurry. The slurry was then heated in an atmosphere of nitrogen gas at a temperature of from room temperature to 850°C while elevating the temperature at a rate of 10°C/min and was maintained at this temperature for 1 hdur. The reaction product obtained was cooled to not more than 100°C, washed with water and dried. Table 2 shows the yield.
Table 1 shows the weight ratio (KOH/M) of potassium hydroxide to mesocarbon microbeads (MCB), and the amount of the water and acetone used. Table 2 shows the properties of the obtained carbon materials Nos. 1 to 11.
Fig. 3 shows an adsoption isotherm determined by subjecting carbon material No. 5 to N₂ gas adsorption method (determined with Autosorb I, manufactured by Yuasa Ionics Kabushiki Kaisha). Fig. 3 clearly indicates that almost all the pores formed are micropores having a radius 0 of up to 10 A.
The properties of the carbon materials as shown in Table 2 were determined as follows. First, the adsorption isotherm was determined by N₂ gas adsorption method (with Autosorb I, manufactured by Yuasa Ionics Kabushiki Kaisha) and then, on the basis of the adsorption isotherm, there were determined (I) BET specific surface area (m²/g), (II) specific surface area of micropores (m²/g), (III) specific surface area of mesopores (m²/g), (IV) total volume of whole pores (ml/g) and (V) volume of the micropores (ml/g). In Fig. 2, the column (VI) shows the yields (wt.%).
Fig. 4 is a graph showing the relationship between the amount of KOH used (weight ratio of KOH/M) and the BET specific surface area of the carbon material obtained in this example.
Although the yield is lowered as the amount of KOH used is increased (the carbon material No. 5 was obtained in a 87% yield, whereas the material No. 11 in 35%), the degree of activation can be desirably adjusted.

Example 2

Carbon materials were each produced in the same manner as done for preparing the material No. 5 of Example 1 with the exception of effecting the activation at a temperature of 400°C, 600°C, 800°C, 1000°C and 1200°C, respectively.
Table 3 shows the properties of the thus obtained carbon materials Nos. 12 to 16.
As seen from Table 3, when KOH is used as an activating auxiliary, it is desirable to conduct the activation at a temperature of about 800 to about 1000°C.

Example 3

Carbon materials were each produced in the same manner as done for preparing the material No. 5 of Example 1 with the exception of using NaOH in place of KOH and effecting the activation at a temperature of 400°C, 600°C and 800°C, respectively.
Table 4 shows the properties of the thus obtained carbon materials Nos. 17 to 19.

Example 4

Carbon materials were each prepared in the same manner as done for producing the material No. 5 of Example 1 with the exeption of using CsOH in lieu of KOH and carrying out the activation at a temperature of 400°C, 600°C and 800°C, respectively.
Table 5 shows the properties of the thus obtained carbon materials Nos. 20 to 22.

Example 5

Carbon materials were each produced in the same manner as done for preparing the material No. 5 of Example 1 with the exception of using K₂SO₄ in place of KOH and performing the activation at a temperature of 400°C, 600°C and 800°C, respectively.
Table 6 shows the properties of the obtained carbon materials Nos. 23 to 25.

Example 6

Carbon materials were each prepared in the same manner as done for preparing the material No. 5 of Example 1 with the exception of using K₂S in lieu of KOH and conducting the activation at a temperature of 400°C, 600°C and 800°C, respectively.
Table 7 shows the properties of the thus produced carbon materials Nos. 26 to 28.

Example 7

Carbon materials were each prepared in the same manner as done for producing the material No. 5 of Example 1 with the exception of using H₃PO₄ in place of KOH and effecting the activation at a temperature of 400°C, 600°C and 800°C, respectively.
Table 8 shows the properties of the thus produced carbon materials Nos. 29 to 31.

Example 8

The same mesocarbon microbeads as used in Example 1 were heated in an atmosphere of H₂0-saturated N₂ gas at a temperature of from room temperature to 800°C while elevating the temperature at a rate of 10°C/min and were maintained at this temperature for 180 minutes, giving a carbon material.
Table 9 shows fhe properties of the thus obatined carbon material No. 32.
The yield of the obtained carbon material was 30% and the BET specific surface area was as small as 64_{0 m}2_/g.

Example 9

Carbon materials were each prepared in the same manner as done for producing the material No. 5 of Example 1 with the exception of using ZnCl₂ in place of KOH and carrying out the activation at a temperature of 400°C, 600°C and 800°C, respectively.
Table 10 shows the properties of the thus produced carbon materials Nos. 33 to 35.

example 10

Using the carbon material No. 3 obtained in Example 1, the equilibrium adsorption amount at 25°C was measured according to JIS K-1474 in respect of benzene, n-pentane, tetrahydrofuran, n-hexane, chloroform, isopentane, cyclohexane, cumene, tetralin, cyclohexylamine, decalin, t-butyl alcohol, trimethylpentane and carbon tetrachloride. Fig. 5 shows the results.
Fig. 5 indicates that the carbon material of the present invention has an ability to achieve such a molecular sieve effect that molecules having a particle size (minor axis) of larger than 4.8 A are likely to be adsorbed only in a slight amount on the carbon material. Accordingly, it is clear that the carbon material of the invention is usable for separating various compounds.

Example 11

The carbon materials No. 8 and No. 11 obtained in Example 1 were tested for occlusion with methane under a pressure of 9 kg/cm² G.
Fig. 11 shows the test results together with a result obtained with use of a known granular activated carbon.
As seen from the results shown in Table 11, it is clear that the carbon material of the present invention has a great adsorptivity.even under an elevated pressure and is therefore usable as an agent for gas occlusion as charged into a gas bomb.

Example 12

A 600 parts quantity of water and 100 parts of acetone were added to a mixture of 100 parts of mesocarbon microbeads which.were the same in particle size distribution as those used in Example 1 and 300 parts of KOH. The resulting mixture was homogeneously stirred, giving a slurry. The slurry was then maintained at a temperature of 800°C for 1 hour in an atmosphere of nitrogen gas, thereafter cooled and washed with water, giving activated mesocarbon microbeads in a 75% yield. The BET specific surface area of the activated mesocarbon microbeads on which N₂ gas was adsorbed was 2054 m²/g, and the proportion of the volume of pores was as shown in Fig. 6.
Subsequently, 15 g of coal-tar pitch was added as a binder to 100 g of the activated mesocarbon microbeads obtained above and the mixture was pelletized by an extruder to pellets 2.5 to 3.0 mm in diameter and 5 to 15 mm in length. The pellets were placed into an oblong column. Styrene vapor diluted to 44% with N₂ gas was introduced into the column maintained at a temperature of 600°C in a ratio (gram) of pellets : styrene = 1 : 3.5, whereby ethylene was polymerized on adsorption in an amount corresponding to 26.9% of the total weight of the pellets. Consequently, the BET specific surface area of the pellets determined with N₂ was reduced to the range of 5.0 to 7.0 m²/g.
Fig. 7 shows the adsorption properties (the amount of the adsorbed gas per gram of the carbon material) of the thus obtained carbon material according to the second present invention in respect of N₂ and 0₂. The curve (A) and the curve (B) each indicate the adsorption properties in respect of 0₂ and N₂, respectively.
Fig. 7 shows that 0₂ was adsorbed rapidly, whereas substantially no amount of N₂ was adsorbed.
In this Example, subsequent Examples and Comparison Examples, the amount of the gas adsorbed was measured with use of the apparatus as shown in Fig. 8. First, a specimen 1 of the carbon material to be checked for the amount of adsorption was set in an electric balance 3 and the pressure in the reaction system was diminished to 10^-2 Torr with a vacuum pump 7 while being heated at 150°C with a heater 5 and held in this state for 1 hour. Then a specific gas was introduced into the system until the pressure therein was changed from 10 Torr to 150 mmHg. Since the gas began to be adsorbed onto the specimen 1 of the carbon material on introduction of the gas, the increase of the amount of the specimen was detected with the electric balance 3 and recorded with the lapse of time with a recorder 17. Various kinds of the gases to be subjected to the adsorption test were each charged into tanks 9-1, 9-2, 9-3, 9-4 and other tanks, respectively. Under such condition, the specimen 1 of the carbon material was replaced with a new one, the system was purged, and the valves of the tanks were changed over, whereby the adsorption properties of two or more kinds of the gases can be determined one after another. In the apparatus shown in Fig. 1, designated 11 is a pressure gauge and indicated at 13 and 15 are traps for collecting water resulting from condensation with use of liquid nitrogen.

Comparison Example 1

Fig. 9 shows the adsorption properties of the commercially available carbon material A having an ability to achieve molecular sieve effect in respect of N₂ and 0₂. The curve (C) and the curve (D) show the adsorption properties in respect of 0₂ and N₂, respectively.
In this case, the difference in the rate of adsorption between O₂ and N₂ is small and therefore the adsorption selectivity of the carbon material is clearly unsatisfactory.

Example 13

Carbon materials were each produced in the same manner as in Example 12 with the exception of supplying styrene vapor in amounts varying within the range of 0.8 to 4.9 g (calculated as styrene) per gram of the pellets used so as to change the amount of the styrene carbonized by adsorption within the range of from 2.1 to 27.8% based on the weight of the pellets.
Shown below is the relationship between the amount of styrene vapor supplied (g/g) and the amount of styrene (%) polymerized and carbonized by adsorption. Also shown are numerals of the corresponding drawings which indicate the adsorption properties of the obtained carbon materials in respect of N₂ and 0₂.
In Figs. 10 to 13, each of the upper curve and the lower curve shows the adsorption properties in respect of 0₂ and N₂, respectively.
These results reveal that each carbon material displays an ability to separate 0₂ and N₂ except for the one obtained in the case in which the amount of styrene polymerized and carbonized by adsorption was 2.1% (Fig. 10).

Comparison Example 2

Carbon materials were each obtained in the same manner as in Example 12 with the exception of maintaining the column containing the pellets at a temperature of 700°C.
However, styrene was pyrolyzed in the gas phase and the pores of the carbon materials were filled up with the pyrolyzed carbon, whereby none of On and N₂ was adsorbed onto the carbon materials.

Example 14

Pellets of the activated mesocarbon microbeads obtained in the same manner as in Example 12 were placed into a column which was oblong, and the vapor of 5-vinyl-2-norbornene diluted to 27% with N₂ gas was introduced into the column maintained at 600°C in a proportion (g) of pellet : steam = 1 : 2.44. This process caused 5-vinyl-2-norbornene to be adsorbed for polymerization and carbonization in an amount corresponding to 18.2% of the total weight of the pellets used.
The BET specific surface area of the thus obtained carbon material with N₂ was reduced to 5.2 m²/g.
Fig. 14 shows the adsorption properties of the carbon material with N₂ and 0₂. In Fig. 14, indicated with the curve (E) and the curve (F) are the adsoption properties with 0₂ and N₂, respectively.
As apparent from Fig. 14, while O₂ was adsorbed rapidly, little amount of N₂ was adsorbed.

Example 15

Using a carbon material obtained by the same procedure as in Example 14, adsorption test was carried out in respect of Ar gas.
The test result was shown with the curve (H) in Fig. 15. Compared with the adsorption property with 0₂ as shown with the curve (G), it is clear that no or little amount of Ar was adsorbed.

Claims

1. A process for preparing active carbon, characterized by activating meso-carbon microbeads.

2. A process according to claim 1 wherein an activating auxiliary is deposited on the surface of meso- carbon microbeads before activation.

3. A process according to claim 2 wherein the activating auxiliary is at least one member selected from the group consisting of KOH, NaOH, CsOH, ZnCl₂, H₃P0₄, K₂S0₄ and K₂S.

4. A process according to claim 2 wherein a surfactant is used in depositing the activating auxiliary.

5. A process according to claim 1 wherein the activation is performed in an oxidizing atmosphere without use of activating auxiliary.

6. Active carbon prepared from activated meso- carbon microbeads and having pores, the active carbon being characterized in that

(i) the carbon is optically anisotropic,

(ii) 90% or more of the whole of carbon consists of particles 80 µm or less in particle size, and

(iii) the micropores of 20 A or less in pore diameter constitute 85% or more of the entire pore volume.

7. A process for preparing a carbon material having an ability to produce molecular sieve effect, characterized in that a vapor of polymerizable organic substance is adsorbed on the surface of activated meso- carbon microbeads and is polymerized on the surface thereof.

8. A process according to claim 7 wherein the polymer being formed during polymerization or the polymer formed thereby is carbonized.

9. A process according to claim 7 wherein the polymerizable organic substance is a vinyl group-containing compound.

10. A carbon material prepared from activated meso-carbon microbeads as the base material, having pores and capable of exhibiting molecular sieve effect, characterized in that

(i) the carbon is optically anisotropic,

(ii) 90% or more of the whole of carbon consists of particles 80 µm or less in particle size,

(iii) the micropores of 20 A or less in pore diameter constitute 85% or more of the entire pore volume; and (iv) the size of pore inlet is reduced by the polymer of polymerizable organic substance adsorbed on the surface thereof.